Spinal interspace shaper

ABSTRACT

A device and method for use in a vertebral spine to prepare a space between adjacent vertebral bodies to receive an implant. The device includes a shaft, and a mounting member at one end of the shaft. A working end is mounted on the mounting member and is coupled to a drive mechanism adjacent to the working end. The drive mechanism is operable to move the upper and lower cutters of the working end to create surfaces having predetermined contours in the end plate region of the adjacent vertebral bodies. A guard provides protected access to the disc space and the adjacent vertebral bodies for the working end of the bone removal device through a passageway.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/779,099,filed Feb. 14, 2004, now U.S. Pat. No. 7,611,514; which is acontinuation of application Ser. No. 09/972,560, filed Oct. 6, 2001, nowU.S. Pat. No. 6,692,501; which claims benefit of Provisional ApplicationNo. 60/255,463, filed Dec. 14, 2000; all of which are incorporated byreference herein.

BACKGROUND

Present methods of forming an implantation space between adjacentvertebral bodies in the human spine generally include the use of one ormore of the following: hand held biting and grasping instruments knownas rongeurs; curettes; drills and drill guides; rotating burrs driven bya motor; and osteotomes and chisels. Sometimes the vertebral end platemust be sacrificed as occurs when a drill is used to drill across thedisc space and deeper into the vertebral bodies than the thickness ofthe bony end plate region. Such a surgical procedure necessarily resultsin the loss of the hardest and strongest bone tissue of the vertebralbodies located in the bony end plate region and thereby removes from thevertebral bodies that portion of its structure best suited to absorbingand supporting the loads placed on those vertebral bodies by aninterbody spinal implant. Nevertheless, the surgeon must work upon theadjacent end plates of the adjacent vertebral bodies to access theunderlying vascular bone that is capable of participating in the fusionby allowing active bone growth, and also to attempt to obtain anappropriately shaped surface in the vertebral bodies to receive theimplant. Because the end plates of the adjacent vertebral bodies are notflat, but rather have a compound curved shape, and because the implants,whether made of bone or any other suitable implant material, whenfabricated or manufactured, tend to have a geometric rather than abiologic shape, it is generally necessary to conform at least a portionof the vertebral bodies to the shape of the implant to be receivedtherebetween.

It is important in forming the space between the adjacent bonestructures to provide a surface contour that closely matches the contourof the implants so as to provide an adequate support surface acrosswhich the load transfer between the adjacent bone structures can beevenly applied. In instances where the surgeon has not been able to formthe appropriately shaped space for receiving the implants, thoseimplants may slip or be forcefully ejected from the space between theadjacent vertebral bodies, or lacking broad contact between the implantand the vertebral bodies, a failure to obtain fusion may occur.

Prior devices having a plurality of rotating cutting elements forremoving bone with a drive mechanism between the cutting elements hadlimitations in certain applications. For example, if the bone to be cutwas thicker than the individual thickness of each of the cuttingelements, then the portion of the device between the cutting elementscould hit the uncut bone and stop the bone removal device from advancingdeeper into the bone being cut. Further, the presence of the drivemember between the cutting elements kept the cutting elements spacedapart and thus could prevent the placement of the bone removal deviceinto very narrow spaces such as, but not limited to, disc spaces asmight be found in some instances in the cervical spine.

There remains therefore a need for an improved spinal interspace shaperthat does not have such limitations so as to achieve the desiredpurposes as described herein.

SUMMARY OF THE INVENTION

The present invention relates to a bone removal device for insertioninto and at least in part across the height of a disc space betweenadjacent vertebral bodies in the human spine, and a guard for providingprotected access to the disc space and for maintaining a desiredpositioning of the adjacent vertebral bodies relative to each other, andto a method of working on those portions of the vertebral bodiesadjacent that disc space to remove bone material sufficient to form adesired contoured end plate and to thereby access the underlyingvascular bone. For purposes of this application, the bony “end plateregion” of the vertebral bodies is defined as the outer shell of compactbone (the bony end plate) adjacent to the spinal disc and the underlyingsubchondral zone.

The apparatus and associated method of the present invention is adaptedto form a surface on or into each of the vertebral body surfaces thatare adjacent the intervertebral disc space. The prepared spaces areformed through the inert outer bone of the vertebral bodies to get tothe vascularized underlying bone, preferably, without generally removingall of the thickness of the end plate region. The formed surface(s) havea defined shape and a contour corresponding to a preferred interbodyspinal implant to be implanted in the disc space.

The bone removal device of the present invention is useful in thecervical, thoracic, and lumbar spine from anterior to the transverseprocesses of the vertebrae, lateral or anterolateral in the thoracic andlumbar spines, or from posterior in the lumbar spine. The bone removaldevice, in a preferred embodiment, generally includes a cutting elementmovably and preferably replaceably mounted on the distal end of a shaft.A depth limiting mechanism preferably controls the depth of insertion ofthe cutting element into the intervertebral space (i.e., the discspace). The device also includes a handle that may be detachable fromthe shaft. As used herein, the term “handle” refers to a portion of thedevice that a surgeon may grip or otherwise manipulate to guide theworking end of the device. That “handle” may in fact have multiplepurposes. For example, the handle may be a portion of the shaft on whichthe working end is mounted at one end. Alternatively, the handle may bepart of a segment that connects the device to a power source. Forexample, the handle may be part of a power source that suppliespressurized gas to the power source if turbine driven, or the handle maybe a drill, but the term “handle” is used herein in its broadest contextto refer to that which the surgeon grasps to use the present invention.

Additionally, the shaft may be detachable from the working end. Thedevice also includes a drive mechanism that transmits power to activate,i.e., move, the cutters. The drive mechanism connects to an energysource, e.g., a rechargeable battery that further may be but need not behoused within the handle of the device. By way of example only, thedrive mechanism may include an electric motor or an electromagneticoscillating mechanism. Or, again by way of example only, the drivemechanism and handle in which it may be disposed may include the headunit of a gas powered turbine of a type commonly used in other surgicalinstruments.

In a preferred embodiment, the working end is generally as wide as thespinal implant to be implanted or the width of a combined plurality ofimplants adapted for side-by-side use between the adjacent vertebralbodies adjacent the disc space. The receiving bed, i.e., the preparedsurface of the vertebral bodies, when formed by the device, willcorrespond in shape, size, and contour to the corresponding surfaces ofa preferred spinal implant or combined width of implants to beimplanted. The surface produced by the bone removal device is generallyflat or concave to correspond to the upper or lower vertebral bodycontacting surfaces of the implant that will be implanted between thevertebral bodies. In an embodiment of the present invention having domedor convex upper and lower cutters or cutting members the device may beinserted into the spine and then turned on to form to desired shape intothe adjacent vertebral bodies. The cutters have a leading end that iscapable of cutting through bone and/or disc material to form a pocket orsocket having a contour corresponding to the forward aspect of theleading end, as well as at least a portion of the side surfaces of thepreferred implant to be implanted. These sidewalls assist in restrainingthe implant from lateral movement.

The working end of the present invention includes a pair of opposed,outwardly facing cutters which lie in planes that may be either parallelto each other or, alternatively, convergent to each other. The presentinvention saves time by simultaneously preparing both of the vertebralend plates adjacent a disc space. The bone removal device shapes thethree-dimensional space created between the adjacent vertebral bodies,which space can be made to conform to the desired lordosis of thatportion of the spine that will receive the implant. The end plate spacemay be, but need not be, identical to the height of the implant, as theimplant may be there to optimize the distance of the disc space.

The drive mechanism of the bone removal device is preferably locatedadjacent the working end of the instrument permitting a reduction in theoverall height of the cutting elements. This configuration permits theoverall height of the cutting mechanism to be thicker or given the sameheight, it can be less than what was previously possible with thecutting elements having a drive member therebetween because the cuttingelements can be placed closer together. A reduced overall height of thecutting mechanism permits the placement of the bone removal device intonarrower spaces, such as but not limited to disc spaces as might befound in some instances in the cervical spine, than previously possible.Moreover, because the space between the cutting elements is minimized,the thickness of the cutting elements may be increased.

The cutting element of the present invention is not limited to being aunitary, one-piece construction, regardless of the number of cuttingsurfaces of the cutting element. The cutting element may includemultiple pieces that, by way of example and not limitation, aremountable on the end of the device to, in combination, define theoverall shape of the cutting element and its surfaces. Thus, the term“cutting element” is used herein to refer to both a unitary, one-piececonstruction or a multi-piece construction.

The cutting element is preferably mounted on the mounting member and maybe removable and interchangeable. In such an embodiment, the mountingmember may be, but does not have to be, attachable to a shaft that isattachable to the handle cutting element and the mounting member may beseparable from each other. Alternatively, the working end and themounting member may, together, be removable from the handle.

While a preferred embodiment of the present invention is discussed anddisclosed herein for creating a space between adjacent vertebral bodiesin the spine, the present invention is not limited to a device forcreating a space between adjacent vertebral bodies, but can also be usedin other portions of the body where it is desirable to place an implantbetween adjacent bone structures. Furthermore, an embodiment of thepresent invention may have upper and lower cutting surfaces that are inangular relationship to each other so as to, for example, match thenatural lordotic curvature of the human spine at the location of thevertebral bodies to be operated upon. Additionally, sequentially larger,that is wider and/or thicker, ones of the cutting elements, or mountingmember, may be used to form the desired sized space in a step-wisefashion, or the working end may be sized to substantially match thefinal desired width of the surface to be formed in the vertebral endplate. Furthermore, the working end is preferably configured with asharpened leading edge to allow the working end to “forward cut” as itis inserted between the adjacent vertebral bodies. In this manner,progressive insertion of the cutting element between the vertebralbodies is facilitated.

In a preferred embodiment, a guard for use with the bone removal devicehas a body with a passageway passing therethrough. In a preferredembodiment, a first disc penetrating extension and a second discpenetrating extension extend from the leading end of the guard and areadapted to be inserted into the disc space between adjacent vertebralbodies. The disc penetrating extensions are preferably adapted todistract and align the disc space, and restore lordosis. The discpenetrating extensions also further limit lateral excursion of the boneremoval device and protect vital structures lateral to the disc space.In the alternative, the guard could be attached with screws or pins toeach of the vertebral bodies like portions to bear upon the end plates.

The guard provides protected access to the disc space and the adjacentvertebral bodies for the working end of the bone removal device througha passageway, which may be sufficiently taller than the height of thespace to be formed by the working end so as to allow for the sequentialuse of working ends of increasing height or the insertion of a spinalimplant taller than the height of the working end thereby allowing thesurgeon the option of keeping the guard in place after the cuttingprocedure. For example, the guard can be left in place distracting andaligning the adjacent vertebral bodies after the cutting step so thatspacers (i.e. trial implants) can be trialed and then the implant of theoptimal height, and perhaps of a greater height than the cutter, can beinserted.

The bone removal device preferably remains appropriately positionedrelative to the height of the passageway during the cut. By way ofexample and not limitation, this may be achieved by having the boneremoval device and guard aligned by a cooperative track, or alongitudinal groove and cooperating protrusion. In an alternativeembodiment, a mounting element may be located between the cuttingportion at the leading end of the bone removal device and the trailingend of the bone removal device. In a preferred embodiment, the mountingelement can be taller than the cutting portion. When the taller mountingelement passes through the passageway of the guard, it contacts theinterior of the passageway to maintain the cutting portion in apreferred orientation to the guard so that the cutting portion can forman implantation space of a height less than the height of the passagewaythat is still properly positioned relative to removing the densethickness of bone from each of the vertebral bodies adjacent the discspace being prepared. This height differential permits an implant havinga height greater than the height of the implantation space to beinserted through the guard. Somewhere along the shaft an enlargedportion may cooperate with the inner height and even the rearwardportion of a guard.

The leading end of the guard may have a foot plate adapted to contactthe vertebral bodies when for use generally anteriorly oranteriorlaterally and may be contoured to generally conform to at leasta portion of the exterior aspect of the vertebral bodies wherecontacted. The foot plate may have holes for receiving, for example,fasteners including spikes, bone screws, pins, prongs, nails, or theequivalent therethrough to secure the foot plate to the vertebral bodiesor such spikes, bone screws, pins, prongs, or nails maybe part of thefoot plate. The attachment of the guard with fasteners to the adjacentvertebral bodies may further secure the vertebral bodies in the desiredrelationship and hold the vertebral bodies steady for the cuttingoperation to be performed.

For use posteriorly, it is generally preferred that the guard have atleast one and more preferably two disc penetrating extensions, such thata foot plate may be minimized or absent.

Thus, the present invention provides a device and method for preparing adisc space between adjacent vertebral bodies to receive a spinalimplant, and prepares that disc space by removing a portion of the bonyend plate region of those vertebrae adjacent that disc space to formpredetermined surfaces in that vertebral bodies adjacent the disc space.The prepared spaces are formed through the inert outer bone of thevertebral bodies to get to the vascularized underlying bone, preferably,generally without removing the full thickness of bone in the end plateregion. The prepared surfaces are sized and contoured to have broadintimate contact with the preferred spinal implant to be implantedbetween the adjacent vertebral bodies and along side walls of a socket,which broad contact provides for increased implant stability. This broadarea of intimate contact between the vertebral bodies and the implantpromotes bone ingrowth from the vertebral bodies into the implant, andalso provides a broad area over which to support the incumbent loads soas to minimize the risk of vertebral collapse or subsidence of theimplant into the vertebra.

While the present invention has been generally described above, and thepreferred embodiments of that invention will be described in detailbelow, neither that general description nor the detailed descriptionlimits the scope of the present invention. That scope is defined by theclaims appearing at the end of this patent specification.

OBJECTS OF THE PRESENT INVENTION

It is an object of certain embodiments of the present invention toprovide a device and method for quickly, safely, effectively, andaccurately working upon the region of the bony vertebral body end plateregions adjacent a disc space so as to, while preferably preserving boneof that region, to at least in part, remove bone such that to access theactive bone growth end plate at least in part, remove bone to produce asocket to accept and implant corresponding in size, shape, and contourto an implant to be implanted between the adjacent vertebral bodies.

It is a further object of certain embodiments of the present invention,to provide a device capable of simultaneously working upon both of thevertebral body end plate regions adjacent a disc space to produceopposed receiving surfaces in the adjacent end plate regionscorresponding in size, shape and contour to a preferred implant to beimplanted, and in so doing to define the shape of the implant space.

It is a further object of certain embodiments of the present inventionto provide a vertebral interspace preparation device that, in apreferred embodiment, is capable of working with linear insertion, i.e.,insertion along a single axis, and without the need to substantiallymove the device from side to side within the disc space along a secondaxis. In such a preferred embodiment, the device has at a working endhaving a width generally corresponding to the width of the implant to beimplanted, and a leading edge corresponding to a generally arcuateleading end of the implant to be implanted, for creating a space of afixed geometry corresponding to an implant of corresponding dimensions.

It is a further object of certain embodiments of the present inventionto have a safety mechanism built into the device that limits the depthof insertion of the device into the spine.

It is a further object of certain embodiments of the present inventionto provide a vertebral interspace preparation device that can haveinterchangeable working ends so as to be capable of producing a varietyof differently sized and contoured surfaces and shapes within theintervertebral space.

It is a further object of certain embodiments of the present inventionto have cutters extending to the leading end of the device such that thedevice may remove bone along its leading end as it is advanced withinthe disc space.

These and other objectives of the present invention will occur to thoseof ordinary skill in the art based on the description of the preferredembodiments of the present invention described below. However, not allembodiments of the inventive features of the present invention needachieve all the objectives identified above, and the invention in itsbroadest aspects is not limited to the preferred embodiments describedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a front elevation view of two disc levels of the lumbar spineshowing the prior art depth of resection resulting from drillingcompletely through the bony end plate region of adjacent vertebralbodies and showing the end plate region on a vertebral body;

FIG. 1B is a top plan view of a spinal interspace shaper bone removaldevice in accordance with one embodiment of the present invention;

FIG. 2 is a side elevation view of the bone removal device of FIG. 1B;

FIG. 3 is an enlarged fragmentary view along line 3 of FIG. 2;

FIG. 3A is an enlarged fragmentary view of the bone removal deviceincluding an alternate embodiment of cutter; FIG. 3B is an enlargedfragmentary view of the bone removal device including another alternateembodiment of cutters;

FIG. 3C is an enlarged fragmentary view of the bone removal deviceincluding yet another alternate embodiment of cutters;

FIG. 4 is a detailed fragmentary view of the cutting portion and drivegears of the spinal interspace shaper bone removal device of FIG. 1B;

FIG. 5 is a trailing end view of an extended guard in accordance withone embodiment of the present invention;

FIG. 6 is a top plan view of the extended guard of FIG. 5;

FIG. 7A is a side elevation view of the extended guard of FIG. 5;

FIG. 7B is a side elevation view of an alternative embodiment ofextended guard;

FIG. 8 is an exploded view of the bone removal device of FIG. 1B,extended guard, and installation screws in accordance with oneembodiment of the present invention;

FIG. 9 is a side elevation view of a human spine with theinstrumentation of FIG. 8 being used from an anterior approach to thespine;

FIG. 10 is a side elevation view of the extended guard being installedfrom an anterior approach into the disc space between two adjacentvertebral bodies and being secured thereto by screws;

FIG. 11 is a partial side sectional view of two adjacent vertebralbodies with the extended guard in partial cross-section installed intothe disc space and secured to the adjacent vertebral bodies byinstallation screws with a bone removal device about to be insertedtherein;

FIG. 12 is a trailing end view of the extended guard of FIG. 11installed into the disc space and secured to the adjacent vertebralbodies by installation screws;

FIG. 13 is a partial side sectional view of two adjacent vertebralbodies with the extended guard of FIG. 11 in partial cross-sectioninstalled into the disc space and secured to the adjacent vertebralbodies by installation screws with a bone removal device insertedtherein and into the disc space;

FIG. 14 is a partial side sectional view of two adjacent vertebralbodies with the extended guard in partial section installed into thedisc space and secured to the adjacent vertebral bodies by installationscrews with the installation space formed across the disc space and intothe adjacent vertebral bodies;

FIG. 15 is a partial side sectional view of two adjacent vertebralbodies with the extended guard of FIG. 11 being removed;

FIG. 16 is a top plan view of an end plate of a lumbar vertebral bodywith an implantation space formed therein from an anterior approach withthe instrumentation and method in accordance with the present invention;

FIG. 17 is a top plan view of an end plate of a cervical vertebral bodywith an implantation space formed therein from an anterior approach withthe instrumentation and method in accordance with the present invention;and

FIG. 18 is a top plan view of an end plate of a lumbar vertebral bodywith implantation spaces formed therein from a posterior approach withthe instrumentation and method in accordance with the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The following description is intended to be representative only and notlimiting. Many variations can be anticipated according to theseteachings, which are included within the scope of the present invention.Reference will now be made in detail to a preferred embodiment of thisinvention, an example of which is illustrated in the accompanyingdrawings.

Human vertebral bodies have a hard outer shell of compacted densecancellous bone (sometimes referred to as the cortex) and a relativelysofter, inner mass of cancellous bone. Just below the cortex adjacentthe disc is a region of bone referred to herein as the “subchondralzone”. As best shown in FIG. 1A, the outer shell of compact bone (thebony end plate) adjacent to the spinal disc and cartilaginous end plateand the underlying subchondral zone are together herein referred to asthe bony “end plate region” and, for the purposes of this application,is hereby so defined. In the lumbar spine the thickness of the cortexend plate adjacent the disc space is generally not greater than severalmillimeters deep. By way of example, prior art threaded implantsrequiring approximately a 3 mm drill depth into the vertebral body andhaving threads of approximately 1 mm or more in height result in a totaldepth of penetration into the vertebral body of at least 4 mmsacrificing the best structural bone adjacent the disc space. Thepresent instrumentation and method permits the preparation of the interspace to receive an implant with less depth of penetration into thevertebral bodies.

FIGS. 1B, 2, 3, and 4 show various views of bone removal device 100 inaccordance with a preferred embodiment of the present invention. FIG. 1Bis a top view of bone removal device 100 and FIG. 2 is a side viewthereof. Bone removal device 100 has a leading end 102 including acutting mechanism 104, and an opposite trailing end 106 configured tocooperatively engage a driving mechanism, such as a power drill,turbine, and the like, or an electrical driving mechanism suitable forthe intended purpose. The particular power source that powers boneremoval device 100 does not form a part of the present invention exceptto the extent it is adapted to achieve the appropriate and desirableamount of movement of the working end, or serves as part of the “handle”when in use.

As shown in FIGS. 1B and 4, cutting mechanism 104 includes a driveelement 108 and a working end 110. Working end 110 preferably includestwo opposed cutters, upper cutter 112 and lower cutter 114 that areconfigured with a sharpened leading edge. In this embodiment, workingend 110 preferably includes two disc-shaped cutting members 116, 118that are removably mounted on the distal end of the device by a recessedconnector 120 and connector shaft 122. Upper cutter 112 is formed on theedge of cutting member 116, and lower cutter 114 is formed on the edgeof cutting member 118. Mounting member 152 facilitates removing cuttingmembers 116, 118 and replacement with other disc-shaped members ofsimilar or alternative cutting or abrading designs. Brace 124 preventsrotation of shaft 126 during use of the device such as by chucking shaft126 into a drill and fitting brace 124 into a non-rotating portion ofthe drill.

In an alternative embodiment, cutters 112, 114 may be manufacturedseparately from cutting members 116, 118. For example, in FIG. 4,disposable or interchangable ring 128 includes upper cutter 112 anddisposable or interchangable ring 130 includes lower cutter 114. Cuttingring 128 is mounted on cutting member 116, and cutting ring 130 ismounted on cutting member 118. Such a mounting may be accomplished bythreadably connecting a cutting ring to its associated cutting member.The threads of such a threadable connection preferably oppose thedirection of rotation of the cutting member when the device is in use.Other equivalent mountings to the threadable connection may be employed,such as where the ends of the wheel are configured such that one endsecures into the other.

Drive element 108 is positioned to rotationally engage working end 110.Drive element 108 is preferably located adjacent to cutting members 116,118. Drive element 108 preferably includes two disc-shaped drive members132, 134 (shown in phantom in FIG. 4). Drive members 132, 134 may beremovably mounted on bone removal device 100 by a connector 136 andconnector shaft 138. Although two disc-shaped elements are preferred, itshould be understood that a number of equivalent structures may be usedto impart rotation to working end 110. For example, instead of two drivemembers 132, 134 as shown in FIG. 4, a hollow or solid cogwheel could beused to interface between working end 110 and a driving mechanism.Another alternative could employ the use of a threaded spindle acting asa drive element. Alternatively, a pulley, spindle, or other rotatingdevice may be coupled to a power source to drive a cord, cable, or belt,or similar power-transferring element to thereby drive cutters 112, 114.Such an alternative embodiment removes the bulk of the drive mechanismfrom between cutters 112, 114 and is within the scope of the presentinvention. It is also possible and within the scope of the presentinvention to angle the cutting elements such that they converge towardsleading end 102 to form an angled cut into the adjacent vertebralbodies. For example, as shown in FIG. 3A, working end 110 can includecutters 112′, 114′ and corresponding cutting members 116′, 118′. Cutters112′, 114′ are tapered relative to one another and converge towardleading end 102. Furthermore, as shown in FIG. 3B, working end 110 caninclude cutters 112″, 114″ and corresponding cutting members 116″, 118″.Cutters 112″, 114″ face outwardly, and are inclined relative to oneanother.

Upper and lower cutting members 116, 118 and their associated cuttersmay rotate in opposite directions so as to mitigate any undesired torqueand to avoid any tendency of the cutting end of the device to movelaterally. This counter-rotating motion may be achieved by using arotating drive rod 140 that extends through shaft 126 and is configuredwith a gear 142 at its distal end that engages with mating gear teeth144, 146 formed on respective sides of drive members 132, 134. Theresulting counter-rotation of drive members 132, 134 (shown by arrows Ain FIG. 4) acts to counter rotate cutting members 116, 118 by way ofcutting member engagement surfaces 148, 150, shown in FIG. 4 as radialteeth. This counter-rotating motion of members 116, 118 is illustratedby the arrows B in FIG. 4. Mating gear teeth 144, 146 may be inwardlysloping, ramped surfaces that engage cone-shaped gear 142 disposed onthe distal end of a rotating drive rod 140 to turn drive members 132,134 in opposite directions as drive rod 140 spins about its axis.Alternatively, cutting member engagement surfaces 148, 150, and driver140 can be radially splined to engage one another or may comprise of anyother known cord, cable, belt or similar power transferring element thatoperatively drives cutters 112, 114.

In the embodiment described, mounting element 152 may interchangeablyreceive various sizes of working end 110 and/or driving element 108.Thus, element 108 and/or working end 110 may be quickly and easilyattached to and detached from mounting member 152 during surgery. Inorder to accommodate the various sizes of working ends and drivingelements, mounting member 152 may be adapted to permit slidableadjustment between shafts 122 and 138. While in a preferred embodiment,upper and lower cutters 112, 114 are selected to have a width that issubstantially the same as the width of the surface to be formed in thevertebral end plate, a surgeon might also elect to use a working end oflesser height than the ultimate desired depth of the surfaces to beformed. Thereafter, the surgeon may use a successively wider and/ortaller work ends of the bone removal device until he arrives at thedesired dimensions of the space formed between the adjacent bonestructures.

The positioning of drive members 132, 134 adjacent to cutting members116, 118, instead of between cutting members 116, 118, permits theoverall thickness of cutting mechanism 104 to be less than waspreviously possible with cutting members 116, 118 having the bulk of adrive member therebetween because cutting members 116, 118 can be placedcloser together. A reduced overall thickness of cutting mechanism 104permits the placement of bone removal device 100 into narrower spaces,such as in narrow disc spaces for example, such as but not limited todisc spaces as might be found in some instances in the cervical spine,than was previously possible. Moreover, because the space betweencutting members 116, 118 is reduced, the thickness of the cutting areamay be increased to permit cutting thicker pieces of bone. For example,in prior devices where a relatively thick portion of the drive mechanismis located between the cutting members, if the bone to be cut is thickerthan the individual thickness of each of the cutting members, then theportion of the device between the cutting members could hit the uncutbone and stop the bone removal device from advancing deeper into thebone being cut.

As shown in FIG. 3, in a preferred embodiment a thin portion 154 ofmounting element 152 extends between cutting members 116, 118 to providesupport and permit attachment of cutting members 116, 118 to mountingelement 152. As shown in FIG. 2, a depth stop 156 having an end 159 forabutting a substrate to be cut, such as for example the exterior of avertebral body, is in slideable engagement to mounting element 152 so asto adjust the depth of penetration of cutting mechanism 104 of boneremoval device 100. An adjusting mechanism 158, such as a spring-biasedlever for example, locks depth stop 156 at the depth selected by thesurgeon. Depth stop 156 also may include an abutment surface or anynumber or shape of projection capable of carrying out the intendedfunction and any known means for securing it. Adjustment mechanism 158may also comprise a number of equivalent structures, such as, forexample, one or more push button spring locks, adjustable turn screws, acollar with spring loaded detents or ball bearings and the like. Brace124 extends from trailing end 106 for holding bone removal device 100 ina desired position relative to the drive means to which it attaches.

In another embodiment, mounting element 152 can be taller than cuttingmembers 116, 118. When the taller mounting element 152 passes throughthe passageway of guard 160, it contacts the interior of the passagewayto maintain the cutting mechanism 104 in a preferred orientation toguard 160 so that cutting mechanism 104 can form an implantation spaceof a height less than the height of the passageway. This heightdifferential permits an implant having a height greater than the heightof the implantation space to be inserted through guard 160.

As a further enhancement to the device it may have evacuation flutes formoving debris proximal. Additionally, an irrigation tube and/or asuction tube may be formed within, or outside of shaft 126. For example,as shown in FIG. 4, a tube 161 for irrigation and/or suction can extendalong shaft 126. These irrigation and suction tubes may be connected toappropriate sources of irrigation fluid and a source of vacuum,respectively, to efficiently irrigate and clear the surgical site duringuse of the device.

Numerous other configurations of working end 110 are possible within thescope of the present invention. For example, upper and lower cutters112′″, 114′″ and corresponding cutting members 116′″, 118′″ may beprovided with, as shown in FIG. 3C, convex portions C1, C2,respectively, to form concave receiving surfaces in the vertebral endplates. The geometry and configuration of the shapes of the upper andlower cutters and cutting members can be matched to the desired shapeand configuration of the space which the surgeon intends to createbetween adjacent bone structures and to the desired contour of thesurfaces created in the bone structures as is disclosed in applicant'sInternational Patent Application No. PCT/US99/12890, filed Jun. 9, 1999,and applicant's U.S. Pat. No. 6,083,228, issued Jul. 4, 2000, both ofwhich are incorporated herein by reference.

Additionally, working end 110 may be configured to have roughenings,knurls, ridges, small pyramid shaped projections, or any other surfaceconfiguration that is capable of cutting or abrading the bonestructures.

FIGS. 5-7A show a guard 160 for use with device 100. In the preferredembodiment, guard 160 has a body 166 with a leading end 162, a trailingend 164 opposite leading end 162, and a passageway 168 passingtherethrough. In a preferred embodiment, a first disc penetratingextension 170 and a second disc penetrating extension 172 extend fromleading end 162. First disc penetrating extension 170 and second discpenetrating extension 172 are adapted to be inserted into the disc spacebetween adjacent vertebral bodies. Guard 160 provides protected accessto the disc space and the adjacent vertebral bodies for working end 110through opening 168. Opening 168 is preferably taller than the height ofworking end 110. Such a taller opening 168 allows the sequential use ofworking ends 110 of increasing thickness or the insertion of a spinalimplant taller than the thickness of working end 110 thereby allowingthe surgeon the option of keeping guard 160 in place after the cuttingoperation. Additionally, body 166 may have a cross section transverse toits longitudinal axis with a complete or incomplete perimeter, (i.e. thecross section may be generally square, rectangular, oval, circular orany other shape with either an open or closed perimeter suitable for theintended purpose). The spinal implant is preferably sized and shaped tomatch the space formed in the spine by the working end.

Leading end 162 of guard 160 preferably has a foot plate 174 (for useanteriorly) adapted to contact the vertebral bodies and may be contouredto generally conform to at least a portion of the exterior aspect of thevertebral bodies in any or all planes. Foot plate 174 preferably isadapted to cover at least a portion of each of the two vertebral bodiesadjacent the disc space into which guard 160 is to be inserted. Footplate 174 may have receiving holes 176, 178 for receiving, for example,fasteners including spikes, bone screws 196, 198, pins, prongs, nails,or the equivalent therethrough to secure foot plate 174 to the vertebralbodies. The attachment of foot plate 174 with screws 196, 198 or theequivalent to the adjacent vertebral bodies may rigidly secure thevertebral bodies in the desired relationship and hold the vertebralbodies steady for the cutting operation to be performed, when the guarddoes not have disc penetrating extensions, or further secure it when itdoes. The disc penetrating extensions may be entirely sufficient bythemselves such that no other means for securing the guard is needed.The example of the foot plate shown in FIGS. 5-8 is suitable for use inthe anterior cervical spine. For use in the lumbar spine, preferablylittle or no foot plate would extend outward from the body of the guard,as the body of the guard itself functions as a depth limiting stop.

Guard 160 also may include one or more guide surfaces along the interiorsurface of passageway 168 to direct cutting mechanism 104 whileaccessing the disc space and adjacent vertebral bodies throughpassageway 168. Such guide surfaces may include any structure designedto direct the cutting mechanism. For example only, such structures caninclude a cooperative track, longitudinal groove, cooperatingprotrusion, and the like. However, it is emphasized that the guidesurface may include any surface designed to direct cutting mechanism104.

As shown in FIG. 8, first disc penetrating extension 170 and second discpenetrating extension 172 have an upper surface 180 and a lower surface182 adapted to contact and support the end plates of the adjacentvertebral bodies. Upper and lower surfaces 180, 182 can be generallyparallel to each other or can be in angular relationship to each other.One or both of upper and lower surfaces 180, 182 may be taperedproximate their insertion end to facilitate insertion of extensions 170,172 into the disc space. An example of a configuration of extensions170, 172 for use in the cervical spine that generally conforms to thebony architecture within the disc space is best shown in FIGS. 7A and11. In the lumbar spine, for use from the posterior approach, extensions170, 172 may have any configuration useful for the intended purposeincluding but not limited to those disclosed in applicant's U.S. Pat.No. 6,080,155 filed Feb. 27, 1995, incorporated herein by reference. Forexample, as shown in FIG. 7B, a guard 160′ is provided including a firstdisc penetrating extension 170′ and an oppositely positioned second discpenetrating extension (not shown).

Guard 160′ (except for first extension 170′ and the second extension)includes the features of guard 160. Furthermore, the second extensionwould be similar in placement to second extension 172, as shown in FIG.6. Both first extension 170′ and the second extension extend fromleading end 162, and include upper and lower surfaces 180′, 182′. Upperand lower surfaces 180′, 182′ have an angular relationship with respectto one another defining a height for first extension 170′ and the secondextension that is lesser at a point proximate leading end 162 thatinitially increases in the direction away from body 166, and then taperstowards their insertion end to facilitate insertion thereof into thedisc space.

While not requisite, extensions 170, 172 (as well as alternativeembodiments thereof) are preferably adapted to distract and align thedisc space, and to restore lordosis. Extensions 170, 172 further limitlateral excursion of bone removal device 100 and protect vitalstructures lateral to the disc space. Trailing end 164 of guard 160cooperates with depth stop 156 of bone removal device 100 to limit thedepth of penetration of cutting mechanism 104 into the disc space. Guard160 assures balanced resection depth of each of the adjacent vertebralbodies and restrains migration of debris generated by the bone removaldevice. As best shown in FIG. 12, after guard 160 is properly positionedrelative to the adjacent vertebral bodies, guard 160 provides thesurgeon a line of sight through passageway 168 to evaluate the boneresection prior to actually performing it. As the length of theextensions 170, 172 are known to the surgeon and are appropriate fortheir intended purpose, the surgeon can, by direct observation,measurement, and/or x-ray, assess the appropriate depth for resectionand implantation. Other shapes of disc penetrating extensions may bedesired and are within the scope of the present invention.

Having described the apparatus, methods for its use will now bedescribed. It should be understood that the order disclosed is onlypreferred and that the steps may be performed in other orders whilestill being within the scope of the present invention. Additionally,some steps may be repeated or omitted as necessary.

Referring to FIGS. 9-15, a method for use in the cervical spine from theanterior approach is described by way of example. As shown in FIG. 9,the correct disc space to be operated upon is identified by the surgeonby direct vision and counting, or preferably, by the use radiographicalimaging with a marker. After the correct disc is identified, guard 160is inserted into the disc space between the adjacent vertebral bodies asshown in FIG. 10.

The disc may have a portion excised and then guard member 160 isinserted such that extensions 170, 172 penetrate the disc space andcontact the adjacent vertebral end plates adjacent that disc space.Guard insertion may be performed over a long distractor such asdisclosed in applicant's U.S. Pat. No. 6,159,214, incorporated herein byreference. It is appreciated that guard 160 may be inserted into thedisc space where the spinal disc is still in place; where at least aportion of the disc has been removed and a distractor is inserted intothe disc space and guard 160 is placed over the distractor; or the guardmay be inserted into the disc space without first using a distractor.

As shown in FIG. 10, extensions 170, 172 of guard 160 are shaped topenetrate the disc space to help secure guard 160 in position to thespine. Extensions 170, 172 may also be beneficial in spacing apart thevertebral bodies, restoring lordosis, or for correcting a relativetranslation of the vertebral bodies. After insertion, guard 160 may be,but need not be, further fixated to the spine by the use of one or morefasteners including screws 196, 198, pins, or other suitable elements,preferably into each of the adjacent vertebral bodies. Again, it shouldbe noted that the presence of foot plate 174 is preferred when the guardis used anteriorly but is not essential.

With reference to FIGS. 11 and 12, the correct depth of the disc spaceto be prepared is determined. The correct disc space depth may bedetermined in a number of ways. For example, the depth may be determinedby pre-operative imaging studies such as plain radiographs, CAT scans,MRIs, and the like. Alternatively, the depth may be determined by directvisualization and/or measurement at the time of surgery, or byintraoperative radiographic monitoring, or any combination of the above.In using radiographic monitoring, for example, a lateral x-ray, thesurgeon can assess the depth of the disc space from the length of eitheror both of extensions 170, 172, and the remaining depth of the discspace. For example, alternatively the surgeon may radiographicallymonitor the progress of cutter mechanism 104 towards the posterioraspect of the vertebral bodies. Additionally, the surgeon by lookingtoward the spine through the passage of the guard can assess the bone tobe resected prior to resecting any bone. Intraoperative radiographicmonitoring will confirm to the surgeon whether the guard is generallyparallel to the disc space, the thickness of the bone to be cut, thedepth of resection for each of the adjacent vertebral bodies, if theguard is centered from side to side, and the depth of extensions intothe space so as to assess the depth of the disc space.

Disc penetrating extensions 170,172 are inserted into the disc space tocontact the adjacent end plates of the vertebral bodies and, if notalready in the desired position, to position the adjacent vertebralbodies in the appropriate distraction and angular orientation to eachother for bone resection. After the adjacent vertebral bodies are in thedesired position, guard 160 may be secured to the spine such that footplate 174 is placed against the anterior aspect of the vertebral bodiesand screws 196, 198 are inserted through holes 176, 178 and into theadjacent vertebral bodies. The adjacent vertebral bodies are held in thedesired position relative to one another during the bone removalprocedure, and if desired, also during the spinal implant insertionprocedure.

Referring to FIG. 13, cutter mechanism 104 is advanced through guard 160into the disc space, removing bone from each of the adjacent vertebralbodies to the desired depth. It should be noted that the progress ofdistal end 102 of the cutter instrument towards the posterior aspects ofthe vertebral bodies may be monitored radiographically for greateraccuracy. The desired depth also may be determined-with adjustable depthstop 156 that may be set to limit the depth of the cutter insertion.Cutter mechanism 104 is then removed. Debris can be removed by suctionand/or irrigation, and optionally with grasping instruments such asrongeurs.

FIG. 14 shows a cutaway side view of adjacent vertebral bodies V₁ and V₂that have had surfaces 184 and 186 formed in their respective adjacentend plates. The remaining portion of the more dense, bony rim 188assists in retaining the spinal implant in the desired position betweenthe adjacent vertebral bodies by acting as an abutment preventinglateral or posterior movement of the spinal implant. The prepared facesof these abutment portions of the vertebral end plate also increase thesurface area of contact between the spinal implant and the vertebralbody. FIG. 14 also shows the cut portion of the disc space being tallerthan extension 172.

After removal of cutting mechanism 104, the surgeon has two optionsdepending upon whether the cutter thickness and the spinal implantheight are similar or not. If the cutter thickness and spinal implantheight are not similar, then the surgeon may elect to remove guard 160as shown in FIG. 15. Next, the correct spinal implant height isdetermined. This determination may be made by knowing the extent ofdistraction prior to cutting, or by trialing the space with spacers todetermine the correct height, or by distracting the space and measuringthe height. Once the implant height has been determined, the correctspinal implant is selected which preferably has a width equal to thespace prepared and a length selected to correspond to the depth of thespace preparation or less, and a height sufficient to restoreappropriate spacing to the inter space. Additionally, the spinal implantis preferably selected to impart a desired amount of lordosis to thevertebral bodies adjacent the interspace.

The spinal implant is then inserted into the prepared space. Duringinsertion, the prepared space may be held at least in part distracted asthe spinal implant is introduced into the prepared space. Preferably,the implant is introduced with an implant driver into the spine andadvanced along the mid-longitudinal axis of the prepared space to thedesired depth by urging it forward as by impaction, and/or pushing itforward, or the equivalent.

If, after removal of cutter mechanism 104, passageway 168 of guard 160has a height as great as the height of the implant to be inserted, thenthe surgeon may insert the spinal implant through guard 160. It shouldbe noted that if the guard was selected to have a passageway heightgreater than the cutter thickness, then the ideal height of the spinalimplant may be determined by introducing into the disc spaceprogressively taller spacers to determine the optimal disc spacedistraction and implant height. After insertion of the implant, theimplant driver, if one was used, is removed.

If the implant is to be inserted without the guard, then guard 160 isremoved from the adjacent vertebral bodies prior to the insertion of theimplant.

Device 100 also may be used in a posterior approach, for example,between the adjacent vertebrae in the lower back, such as L₁ through S₁,from a posterior approach, or from posterior to the transverse processesof the vertebrae, including both straight posterior and posterolateral.If a posterior approach is used, many of the above steps apply. In orderto position guard 160, the dural sac is retracted towards the sideopposite of the insertion and protected along with the traversing nerveroot. For easier visualization of the area to be resected, guard 160 mayinclude inspection slots placed away from tissues such as the dural sacand nerves that need to be protected. Guard 160 is preferably placed toone side of the midline, that is, the line separating right and lefthalves of the vertebral bodies, especially when the surgeon intends toplace an implant on each side of the midline. During the posteriorapproach, the surgeon will normally prefer to place two implants, eachhaving a maximum width less than half of the width of the disc space andgenerally oriented from the back to the front of the disc space, orslightly toed in. Alternatively, the surgeon may elect to place but asingle implant. In such instance, the single implant may be placed morediagonally across the disc space allowing for the use of a longerimplant, or to place two implants from the same side.

In a posterior lateral approach, no laminar bone need be removed as thedisc space is entered lateral to the spinal canal. In that case, twotoed-in implants can be used or a single implant placed diagonally whichmay be longer than when the two are used. As the disc penetratingextensions themselves (the part in the disc) can be of various crosssectional shapes it may be preferred to utilize a distractor having aheight greater than its width so that it can be introduced on its sideand then rotated 90° to its height. In that case, it is preferred thatat least one of the diagonals, if not both, be reduced in length byreduction of the junctions or corners where the top and bottom meet thesides. Alternatively, the trial spacers may resemble the implant inshape, though it may be preferred to leave the bone engaging surfacessmooth to facilitate removing the trial implants or distractors. As usedherein, the term trials refers to spacers that are similar to an implantin shape but without a bone engaging surface such that it is smooth andlesser in height than an implant and used to determine the appropriatetension for the disc space in which a spinal implant is to be inserted.

FIGS. 16-18 illustrate various views of vertebral bodies withimplantation spaces that have been prepared by a device incorporatingthe present invention. The cross-hatching in these figures representsthe machined areas of vascular bone. FIG. 16 shows a top view of a firstvertebral body V₁ such as in the lumbar spine where the depth ofresection is sufficient to allow for the full diameter of the cutter topass into the disc space, leaving parallel straight sides and anatomiccontour at the trailing (anterior) aspect of the vertebral body. Thecreated space includes a leading portion adapted to correspond to theleading end of an implant and sides adapted to correspond to at least aportion of the sides of the implant. First vertebral body V₁ has asurface 190 formed by working end 110 as shown in FIG. 4. The width ofsurface 190 formed on first vertebral body V₁ closely matches the widthof working end 110 that was advanced into the disc space along a singlefront to back axis.

FIG. 17 shows the top view of a second vertebral body V₂ such as in thecervical spine where the depth of resection may be limited such that thefull diameter of the cutter never passes into the bone. The createdspace is adapted to correspond to at least a portion of the leading endof the implant and possibly a portion of the sides.

FIG. 18 shows the top view of a lumbar vertebral body V₃ showingside-by-side passes of the hemi-width cutter from a posterior toanterior approach. In such an instance, the cutter preferably has amaximum width of less than half the width of the disc space. Theprepared areas may or may not touch each other.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

1. A system for preparing a space in the human spine to receive animplant between adjacent vertebral bodies, said system comprising: abone removal device comprising: a shaft having a proximal end, a distalend opposite said proximal end, and a mid-longitudinal axistherebetween; at least a first and a second cutter sized and shaped toremove bone from the adjacent vertebral body endplates simultaneously assaid first and second cutters are moved to create an implantation space,each of said first and second cutters having a leading end and anopposite trailing end, said leading ends of said first and secondcutters defining a forward facing cutting area having a maximum heightas measured along a line passing through said leading end of each ofsaid first and second cutters and transverse to the mid-longitudinalaxis of said shaft; a drive element having a leading portion and atrailing portion opposite said leading portion, said leading portion ofsaid drive element connecting to said trailing ends of said first andsecond cutters for moving said first and second cutters, at least aportion of said distal end of said shaft and said leading portion ofsaid drive element each having a maximum height transverse to themid-longitudinal axis of said shaft not greater than the maximum heightof said forward facing cutting area of said first and second cutters,said at least a portion of said distal end of said shaft and saidleading portion of said drive element each being located within and notextending beyond the maximum height of said forward facing cutting areaof said cutters; and a power source operably connected to said driveelement; and a guard for providing protected access to the adjacentvertebral bodies, said guard comprising a body having a leading end, atrailing end opposite said leading end, a mid-longitudinal axistherebetween, and an opening passing through said leading and trailingends, said opening having a height and a width transverse to and greaterthan said height, said height of said opening being greater than themaximum height of the forward facing cutting area of said bone removaldevice, said opening being sized and shaped to permit said first andsecond cutters to pass through said body and access the vertebral bodyendplates.
 2. The system of claim 1, wherein said first and secondcutters include teeth formed thereon to cooperatively engage said driveelement, said drive element and said teeth being configured such thatsaid first and second cutters are rotated by said drive element.
 3. Thesystem of claim 1, wherein said first and second cutters are adapted tobe rotated in opposite directions by said drive element.
 4. The systemof claim 1, wherein at least one of said first and second cutters has awidth, said width substantially matching the width of the nucleuspulposus of a disc space in which it is inserted.
 5. The system of claim1, wherein said first and second cutters are inclined relative to oneanother.
 6. The system of claim 1, wherein said first and second cuttersare driven in a reciprocating, arcuate motion by said drive element. 7.The system of claim 1, wherein said drive element is adapted to producea rotary movement of said first and second cutters about an axisgenerally perpendicular to the mid-longitudinal axis of said shaft. 8.The system of claim 1, wherein said drive element is adapted to produceone of an oscillating rotation and a vibratory motion of said first andsecond cutters.
 9. The system of claim 1, wherein said guard furtherincludes a foot plate sized and shaped to contact at least a portion ofeach of the adjacent vertebral bodies, said foot plate having at leastone opening configured to receive a fastener adapted to secure said footplate to the vertebral bodies.
 10. The system of claim 1, wherein saidguard further comprises first and second disc penetrating extensionsextending from said guard for insertion into the disc space between theadjacent vertebral bodies, each of said disc penetrating extensionshaving a portion for bearing against each of the adjacent end plates ofthe adjacent vertebral bodies, each of said portions of said discpenetrating extensions having an upper surface adapted to contact one ofthe adjacent end plates of the adjacent vertebral bodies and a lowersurface adapted to contact the other of the adjacent end plates of theadjacent vertebral bodies, said portions of said disc penetratingextensions having a height between said upper and lower surfaces and alength sufficient to properly align and distance apart the adjacentvertebral bodies.
 11. The system of claim 10, wherein said upper andlower surfaces are parallel to each other along a substantial portion ofthe length of said portions.
 12. The system of claim 10, wherein saiddisc penetrating extensions are diametrically opposed to each other andspaced apart from one another to provide access to the adjacentvertebral bodies from within the disc space.
 13. The system of claim 10,wherein the height of said disc penetrating extensions have at least aportion that approximates the height of a normal disc space between theadjacent vertebral bodies.
 14. The system of claim 10, wherein said discpenetrating extensions have a tapered leading end to facilitateplacement of said disc penetrating extensions into the disc space, saidportion of said disc penetrating extensions having opposite surfaces forbearing against the end plates of the adjacent vertebral bodies, saidopposite surfaces diverging away from said guard along at least aportion of their length.
 15. The system of claim 10, wherein said upperand lower surfaces converge away from said guard along at least aportion of their length.
 16. The system of claim 10, wherein saidopening of said guard has an interior having a cooperating surface forguiding a corresponding cooperating surface of said first and secondcutters.
 17. The system of claim 1, in combination with an implant sizedand shaped to match the implantation space formed in the spine by saidfirst and second cutters.
 18. The system of claim 17, wherein saidimplant is one of a spinal implant and a spacer.
 19. The system of claim1, wherein at least a portion of said first and second cutters areseparated by a space and substantially overlie one another, said driveelement being configured to engage said first and second cutters outsidethe space separating said cutters.
 20. The system of claim 1, wherein atleast a portion of said first and second cutters is operativelyconnected to said drive element in a plane parallel to themid-longitudinal axis of said shaft.